This invention relates to piezoelectric materials and, more particularly, to electrically poled .gamma.-phase nylon 11 which has desirable piezoelectric characteristics, to be used in acoustic transducers and the like.
Certain polymers have been found to exhibit high piezoelectric activity and have the advantage that they can be formed into films and other desirable shapes. Since the initial discovery of the large piezoelectric response of poled, oriented films of PVF.sub.2 by Kawai in 1969, several subsequent studies have been made to explain the mechanisms responsible for this phenomenon. As the greatest piezoelectric activity has been found for PVF.sub.2 films, extensive work has been done in the prior art to fabricate various forms of PVF.sub.2 polymer and various explanations have been put forward to explain their piezoelectric properties. Mechanisms most often discussed are: a bulk polarization of the sample due to field induced reorientation or switching of the molecular dipoles in the polymer crystals; non-uniform charge injection producing an asymmetric distribution of real charge in the sample; a field induced trapping of injected or ionic charges present as impurities; and some type of surface phenomenon caused by the strong interaction between the positive electrode and the film during poling. Furthermore, efforts have also be made to explore new polymeric materials which exhibit piezoelectric characteristics. As an example, odd nylons have been studied for their piezoelectric behavior by various people. However, little attention has been given to .gamma.-phase nylon because of its non-polar crystalline structure. However, nylon 11 has been studied in its .alpha.-phase configuration because of its polar crystalline structure. But .alpha.-phase exhibits very low piezoelectric properties. It is thus desirable to explore further any useful behavior exhibited by odd nylons in general, and nylon 11 (.gamma.-phase) in particular, despite the generally held view of its non-polar crystalline structure.